Mixed wettability surfaces strongly influence droplet departure in surface engineering applications. Although homogeneous superhydrophobic surfaces provide optimal removal performance, real surfaces typically exhibit heterogeneous wettability. Here, we investigate droplet departure mechanisms on smooth surfaces with alternating wettability patches using a multicomponent pseudopotential lattice-Boltzmann method. Gravity-driven pendant detachment and gravity-assisted coalescence-induced departure are examined over a wide range of heterogeneity length scales relative to droplet wetted base length ( a/w) and size ( a/R-eq). Results show that homogeneous surfaces generally exhibit lower critical Eotvos numbers ( Eo(crit)) than heterogeneous surfaces, with heterogeneity increasing the detachment threshold by approximately 5% and 16% for pendant and coalescence-induced departure, respectively. For pendant droplets, increasing a/w shifts detachment from continuous contact-line recession to pinch-off at a/w approximate to 1; in this regime, Eo(crit) increases monotonically up to 15% on net hydrophobic surfaces ( theta(eff)=141 degrees) but decreases by approximately 8% at larger patch length scales under near-neutral wetting ( theta(eff)=105 degrees). For coalescence-induced departure, a competition between droplet coalescence and contact line jumping governs detachment behavior when a/R-eq approximate to 0.06. In this regime, frequent stick-slip dynamics promote premature contact line jumping, which increases Eocrit by 20%. Under the Cassie framework of chemically inhomogeneous surfaces, strong heterogeneity can instead enhance droplet removal through controlled contact-line pinning, increasing droplet detachment performance up to 28%. A hysteresis analysis accounts for these effects of patch wettability contrasts, while a new proposed viscous-dissipation-based framework offers a preliminary mechanistic explanation for the influence of relative patch length on droplet departure.
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